Considerable evidence has accumulated to suggest that startle, a reflex response to stimuli with abrupt onset, is a sensitive index of vulnerability to increased anxiety for states of arousal and that individual variation in the startle response under varying conditions provides a window on the development of centrally based mechanisms for arousal and state regulation. A laboratory has been established for assessment of the startle response in children ages 3 - 18. The developmental maturation of affectively (or "fear") potentiated and prepulse inhibition of the startle reflex is being examined. The startle response is also being examined in a group of prenatally cocaine-exposed children already involved in an ongoing longitudinal study of the developmental effects of early cocaine exposure. Evidence from the PI's and others' work suggest that the startle reflex may be increased among cocaine-exposed children.